YES! Oh, YES! I have finally figured out how to make my NES display in RGB! Ok, first thing is you cant make a stock NES display RGB, you have to add some special parts, most notably a special new PPU chip. I have been looking at some diagrams for the Playchoice 10 (an arcade version of the NES with a timer so you can pay to play), and after deciphering the non-standard pin nomenclature that the Japanese designers used I have been able to figure out exactly what needs to be done to swap out the NES PPU with the PPU from a Playchoice 10. I will be hunting ebay for a PC10 sometime soon, hopefully I can get one cheap.
Anyhoo, here is what you gotta do so swap the NES PPU with the PC10 PPU. The pinout for these chips are exactly the same, except for a few differences. Pins 14,15,16,17, and 21 are the only ones which differ. On the NES PPU, pins 14-17 do nothing, and are always conected to ground. Look on the NES for the four pins that are all on the same ground bus, and those are the ones I am talking about.
On the playchoice 10, those pins are (from 14 to 17) Red, Green, Blue, and Video Ground respectively.
Pin 21 is normally the composite video out on the NES PPU, but on the PC10 it becomes the Sync pin.
So, to swap the chips you need to take out the NES PPU, plop in the PC10 ppu, and bend up pins 14-17 and 21 and attach flying leads to those pins. Then its a snap to wire up the signals wherever you want them to go.
Conversely, you could convert a PC10 to play on a normal TV by putting the NES PPU into it, with much the same procedure. Maybe I should do both mods at the same time, a RGB mod for my portable and an NTSC mod for the arcade board.
Tell me what you think guys!
RGB on the NES (famicom)
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Emulation isn't accurate. There is no substitute for real hardware!
OK, I did a little digging around, and there is only a veeery small difference in the pallete setup between the NES and the PC10, there are a few usually unused shades of grey missing, and color emphasis doesn't work the same way, but thats ok because most NES games dont use color emphasis at all. The only NES software I know of that fully utilizes color emphasis is homebrew, so thats OK, since most homebrew NES stuff cant really be played anyway.
Emulation isn't accurate. There is no substitute for real hardware!
Yah, I just put a replacement guide on the forums at NESdev. Its really easy too. I want to mod up a famicom and make a portable out of it. RGB on my portable is just what I want! Plus, it would be wicked awesome and NOBODY else would have it! 
Mwahahahaha!
Mwahahahaha!Emulation isn't accurate. There is no substitute for real hardware!